Electrical condenser



May 30, 1950 F. BROCKMAN 2,509,758

ELECTRICAL CONDENSER Filed Jan. 26, 1949 100000 [DIELECTRIC CONSTANT ivs.

TEMPERATURE soooo MAGNETIC 40000 CURIE POINT TEMPERATURE 1N DEGREESCENTIGRADE FIGJ CAPACITOR DIELECTRIC CDNSTITUTED BY A MIXED CRYSTALFERRITE FIG-2 FRANK BROCKMAH INVENTOR AGENT Y Patented May 30,

ELECTRICAL CONDENSER Frank Brockman. Dobbs Ferry, N. Y., assignor toPhilips Laboratories, Inc., Irvington on Hudson,

Application January 26, 1949, Serial No. 72,959

8 Claims. 1

My invention relates to electrical condensers.

It is an object of my invention to provide a new and novel electricalcondenser.

It is a further object of my invention to provide a temperatureresponsive electrical condenser having improved characteristics.

These and further objects of my invention will appear as thespecification progresses.

The electrical condenser according to my invention comprises twoelectrodes and a dielectric of a ferromagnetic core material consistingessentially of mixed crystal ferrites of selected metal oxides. Suchmaterials, which are described in the U. S. Patents 2,452,529; 2,452,530and 2,452,531 dated October 26, 1948 to J. L. Snoek, consist of mixedcrystals of a plurality of oxides of bivalent materials mixed andreacted with iron oxide.

Electrical condensers according to my invention exhibit an unexpectedlyhigh capacitance for a given size, and I have found that this is due tothe fact that such materials have unexpectedly high dielectric constantswhich are greater than 100 and in some instances of the order of 10 to10 In addition, my electrical condensers have the further advantage thatthey have a large absolute variation capacity with changes intemperature and I have found that this is due to the unusual temperaturedependence of the dielectric constant of such materials.

' decreases until it nears the magnetic Curie tem- In order that theinvention may be more clearly understood and carried into effect, itwill now be described with reference to the accompanying drawing inwhich:

Fig. l is a curve indicating the dependence of the dielectric constantof the dielectric on temperature; and

Fig. 2 is a capacitor according to the invention.

Referring to the drawing, I have shown in Fig. l the temperaturedependence of the dielectric constant of a particular mixed crystalferrite, i. e., manganese-zinc ferrite the constituent components ofwhich consist for example of about 23 mol per cent manganese oxide,about 25 mol per cent zinc oxide and about 52 mol per cent iron oxide.Although the invention will be described with reference to thisparticular material, I wish it to be understood that other mixed crystalferrites described in the above-identified patents are suitable for theinvention, e. g. copperzinc ferrite, magnesium-zinc ferrite,coppercadmium ferrite and nickel-zinc ferrite.

Referring to Fig. 1, the ordinates are specified in values of thedielectric constant E and the abscissae in degrees centigrade oftemperature.

It should be noted that the curve is a measure of the real part of thedielectric constant, an imaginary part not being shown since it in noway influences the character of the invention. To those familiar in theart, it is known that at higher frequencies, e. g. above one megacycle,the true dielectric constant of a material is composed of a real partand imaginary component corresponding to the real and imaginary parts ofa complex argument of a mathematical function.

It will be seen from the curve that the dielectric constant attemperatures below the temperature indicated as the magnetic Curiepoint, has a value of the order of 10 and gradually perature. In' theneighborhood of the magnetic Curie temperature, the dielectric constantdecreases rapidly. Quite unexpectedly I found that in the vicinity ofthe magnetic Curie temperature the dielectric constant rises verysharply and levels off at a lower value than the initial value of thedielectric constant at the start of the curve.

The Curie point of a magnetic material is that temperature above whichthe magnetic material has a negligible permeability and for allpractical purposes is no longer ferromagnetic. The Curie point offerromagnetic mixed crystal ferrite materials to which the presentinvention is directed can be controlled over a wide range oftemperatures as set forth in the above noted patents and therefore thetemperature at which the dielectric constant of the materials exhibits asharp drop in value as well as the slope of the change in dielectricconstant with temperature over a given operating temperature range cansimilarly be controlled.

The condenser shown in Fig. 2 comprises a dielectric l in the form of adisc and consisting essentially of a mixed crystal ferrite as abovedescribed and electrodes 22 consisting for example of metal layers ofsilver, copper, gold, lead, tin or the like positioned on the dielectricby spraying, firing or the like. When utilizing as a dielectric themanganese-zinc ferrite above specifically described, the condenserexhibits a negative temperature coefficient of capacity over thetemperature range below the magnetic Curie point, i. e. over thetemperature range between 20 and C. At the magnetic Curie temperature asharp reversal in the temperature 00- efiicient occurs and within atemperature change of approximately one degree a large change incapacitance occurs.

Such capacitors would be useful for numerous applications. For example.the capacitor described is useful in radio circuits as a temperaturecompensating capacitor for correcting undesirable frequency drift due totemperature changes of the circuit components. Furthermore the capacitoris suitable as a, temperature responsive switch because of the abruptchange in capacitance over a small temperature rangei. e. of the orderof 1 C., which it undergoes at temperatures about the magnetic Curiepoint.

Where a large capacitance per unit volume is desired. the unexpectedlyhigh dielectric constant of the material makes these condensersparticularly useful.

As above noted the magnetic Curie temperature of the ferrites can becontrolled to any desired value as described by J. L. Snoek in theabove-identified patents which therefore renders possible capacitors ofvarying characteristics each suited to a particular desired application.

While I have thus described my invention with specific examples andapplications, I do not wish to be limited solely thereto as othermodifications will be apparent to those skilled in the art withoutdeparting from the spirit and scope of the invention.

What I claim is:

1. An electrical condenser comprising a pair of electrodes and adielectric therebetween consisting essentially of a mixed spine] crystalferrite material.

2. An electrical condenser comprising a pair of electrodes and adielectric therebetween consisting essentially of a ferromagnetic mixedspinel crystal ferrite material.

3. An electrical condenser comprising a pair of electrodes and adielectric therebetween consisting essentially of a ferromagnetic mixedspinel crystal ferrite material having a dielectric constant greaterthan 100.

4. An electrical condenser comprising a pair of electrodes and adielectric therebetween consisting essentially of a ferromagnetic mixedspinel crystal ferrite material having a dielectric constant of theorder of 10 5. An electrical condenser comprising a pair of electrodesand a dielectric therebetween consisting essentially of mixed crystalsof manganesezinc ferrite having a dielectric constant of the order of 106. An electrical condenser comprising a pair of electrodes and adielectric therebetween consisting essentially of mixed crystals ofmanganesezinc ferrite, said dielectric having a. magnetic Curie pointwithin the normal operating range of temperatures of the condenser andhaving a dielectric constant of the order of 10 7. An electricalcondenser comprising a pair of electrodes and a dielectric therebetweenconsisting essentially of mixed crystals of manganesezinc ferrite, saiddielectric having a magnetic Curie point at about C. and having adielectric constant of the order of 10 8. An electrical condensercomprising a pair of electrodes and a dielectric therebetween consistingessentially of mixed crystals of manganesezinc ferrite, said dielectrichaving a magnetic Curie point at about 160 C. and exhibiting a sharprise in the value of the dielectric constant at the said temperature,said dielectric having a dielectric constant of the order of 10 FRANKBROCKMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Snoek .'Oct. 26, 1948

1. AN ELECTRICAL CONDENSER COMPRISING A PAIR OF ELECTRODES AND ADIELECTRIC THEREBETWEEN CONSISTING ESSENTIALLY OF A MIXED SPINEL CRYSTALFERRITE MATERIAL.